With regular season arriving, Bears' issues on defense far from solved.

As the calendar flipped to September, the Bears marched into Week 1 of the regular season Monday, eager to attack this weekend's opener with the Bills. But 40 days after training camp opened, coach Marc Trestman probably would prefer even more time to get everything settled before meaningful game action begins.

After all, when the Bears took the practice field Monday at Halas Hall, several signs of instability were obvious. For starters, long snapper Jeremy Cain was the newest face on the 53-man roster, a Monday morning signing as the team's latest bandage on a special teams problem that has been hemorrhaging since Patrick Mannelly's June retirement.

The safety situation isn't much better with Trestman acknowledging he's still taking the "wait and see" path toward finalizing a starting tandem.

And adding to the Week 1 confusion, linebacker Lance Briggs was absent from the facility Monday, excused by Trestman for what the team classified as "personal reasons." That explanation seemed harmless enough — until you consider the 12th-year veteran and seven-time Pro Bowl selection was in California on Monday, helping emcee the grand opening of his Double Nickel Smokehouse, an event he had been actively promoting on Twitter.

Asked about Briggs' absence, Trestman said he had no worries.

"I had communication with him three weeks ago about it," the Bears coach said. "We talked about it. And I excused him for personal reasons. So this is not something that happened yesterday or the day before. He contacted me a couple weeks ago and I said, 'Yeah, you can go.' That was it."

Trestman would not confirm, however, whether his top linebacker missed the first practice of the regular season's first week solely because of a restaurant venture.

"I'm not going to speak for him with what he's doing today," Trestman said. "I can tell you that I excused him. ... Where he's gone is between him and the reasons why he had to go. But it was good by me."

The Tribune's Dan Wiederer and Rich Campbell discuss the Bears' impending decision on their starting safeties.

The Tribune's Dan Wiederer and Rich Campbell discuss the Bears' impending decision on their starting safeties.

The Bears will need Briggs at his sharpest Sunday to stabilize a defense that enters the regular season with more disorder than they hoped to have at this stage. Uncertainty at both safety and linebacker remains. And the first-unit defense is coming off an uneven preseason that lacked convincing evidence of dramatic improvement.

"There's always concern," cornerback Tim Jennings admitted. "But I think we're going to have our guys hyped up, ready to go. (Sunday's) a full game. We're not going to just play a quarter here, two quarters here. We're going to play a whole 60 minutes of football. So this first one is a good test to see where we're at."

At full strength, the Bears feel like they've made significant strides from the end of last season, when the defense allowed 430.5 yards and 35.2 points per game over the final six weeks. But the exhibition season didn't offer extended opportunity to showcase what full strength looks like now.

The Bears on Monday filled their long-snapper vacancy by signing Jeremy Cain for a third stint with the team.

Cain was the Bears' long snapper last season for two games, including a muddy overtime win over the Ravens on Nov. 17. In those games, he replaced Patrick Mannelly, who sat out with a calf...

Defensive end Jared Allen played only 28 preseason snaps, all against the Jaguars on Aug. 14. Rookie cornerback Kyle Fuller logged only 35 preseason snaps on defense, all against the Eagles a week earlier.

Jennings, meanwhile, missed that Eagles game with a quadriceps issue. So there was no point in the preseason when all 11 starters plus key reserves Fuller and linebacker Jon Bostic were active together.

So what gives Jennings hope that the defense can quickly round into form?

"We're hungry," he said. "We've got attitude from (what happened) last year. The coaches feel the same way as well as the players do. The attitude we have is setting the tone. … We've still got the same mentality. The more takeaways we get to give our offense back the ball, we can put more points on the board."

Still, last season's collapse plus an ordinary August had led to growing outside worry that the defense will remain a significant weakness.

"I don't feel that trepidation," Trestman countered. "We're going to have to come together. It's going to be a process working together, getting to know each other and how each other works. But the talent level is there."